Point-to-multipoint communication systems provide communications generally between a central location and multiple users of the system. For example, dispatch systems using Land Mobile Radios (LMRs) have been used in trucks, taxis, buses, and other vehicles in order to communicate scheduling information between a central dispatch center and one or more corresponding fleet vehicles. Communications may be directed at a specific vehicle in the fleet or to all vehicles simultaneously.
A class of wireless services intended for quick, efficient, one-to-one or one-to-many (group) communication operates in half-duplex communication, using a forward link or a reverse link at a time. A user presses a “push-to-talk” (PTT) button on a phone/radio to initiate a group communication. If granted the floor, the user provides media for a short time period. After the user releases the PTT button, other users may request the floor. These services have traditionally been used in applications where one person, a “dispatcher,” needs to communicate with a group of people, such as field service personnel or taxi drivers. Similar services have been offered on the Internet and are generally known as “voice chat.”
A key feature of these services is that communication is quick and spontaneous, usually initiated by simply pressing a PTT button, without going through a typical dialing and ringing sequence. Communication in this type of service is generally very short, with individual media “spurts” being generally on the order of several seconds, and “communications” lasting possibly a minute or less. The time delay between when the user requests the floor and when the user receives a positive or negative confirmation from a communication manager, indicating that the user has the floor and may begin providing media, is known as PTT latency.
PTT half-duplex communication offers a number of advantages, such as improved bandwidth efficiency, reduced sensitivity to latency, and simplified echo cancellation.
There is a need, therefore, for concurrent communication of multimedia, e.g., audio, video, image and/or data, in half duplex mode, which provides the advantages of PTT group communication services.